Non-fusion scoliosis expandable spinal rod

ABSTRACT

A growing rod for mounting between attachment mechanisms that are secured to anatomical structures of a patient having scoliosis. The growing rod includes an outer housing and an inner housing disposed within the outer housing. The inner housing includes a magnet assembly including a magnet having a first pole and a second pole and a gear reduction mechanism coupled to the magnet. A first rod is secured to the inner housing and a second rod is secured to the outer housing. The gear reduction mechanism reduces an output rotation of the magnet to rotate a driver that operates to move the inner housing along a longitudinal axis with respect to the outer housing.

CROSS-REFERENCE TO RELATED APPLICATION

The present disclosure is a continuation of U.S. patent application Ser.No. 13/302,187, filed Nov. 22, 2011, entitled “Non-Fusion ScoliosisExpandable Spinal Rod,” which claims priority to which claims priorityto U.S. Patent Application Ser. No. 61/416,266, filed Nov. 22, 2010,entitled “Non-Fusion Scoliosis Expandable Spinal Rod,” which isincorporated herein by reference in its entirety.

BACKGROUND OF THE DISCLOSURE

Scoliosis is a medical condition where an individual's spine curves offof its anatomical shape, typically in an “S” or “C” shape, and may alsobe rotated about a vertical axis or a longitudinal axis of the spine.Scoliosis can be a particularly painful and dangerous condition foryoung persons including infants, juveniles and adolescents, who are notfully grown. Young persons with scoliosis may be treated in variousmanners depending upon age, severity of the curve and the likelihood ofprogression of the condition. Conventional options for scoliosis includeobservation, bracing and surgery.

Surgery is typically indicated for juvenile scoliosis when there is ahigh likelihood of progression, the curve is causing significant painand/or the curve is impacting physiological functions, such asbreathing. Surgical intervention typically results in fusion of theimpacted portion of the spine, which is ideally delayed until thepatient is skeletally mature. However, certain severe cases of juvenilescoliosis require surgical intervention prior to skeletal maturity toprevent progression of the curve and/or to stabilize the spine. Multiplesurgeries in such cases are common to gradually correct the curvatureand/or modify the surgical construct to permit growth or to graduallymove the curved or twisted spine.

SUMMARY

The present disclosure relates generally to orthopedics. Morespecifically, the disclosure relates to a non-fusion scoliosis constructincluding a magnetically actuated growing rod that permits extension ofthe rod, growth of the construct and extension or correction of apatient's spine without significantly invasive surgical intervention.The device includes an actively expandable rod that is mounted to apatient's spine or ribs using hooks, screws and/or other fasteningmechanisms to be fixed to the posterior of the patient's spine or tonearly any other portion of the patient's spine that permits correctionof an undesirable spinal curvature. The system is preferablymagnetically activated from outside of the patient's body utilizing amagnetic field without further surgery for expansion.

In accordance with some implementations, there is provided a growing rodfor mounting between attachment mechanisms that are secured toanatomical structures of a patient having scoliosis. The growing rod mayinclude an outer housing, an inner housing disposed within the outerhousing, and a magnet assembly rotably mounted within the inner housing.The magnet assembly may include a magnet having a first pole and asecond pole. A gear reduction mechanism may be coupled to the magnetwithin the inner housing. The gear reduction mechanism reduces an outputrotation of the magnet to rotate a driver that operates to move theinner housing along a longitudinal axis with respect to the outerhousing. The growing rod may include an interchangeable first rodattached to the inner housing and an interchangeable second rod attachedto the outer housing.

In accordance with some implementations, there is provided a drivemechanism for a growing rod. The drive mechanism may include an innerhousing comprising a magnet assembly including a magnet having a firstpole and a second pole and a gear reduction mechanism coupled to themagnet, the gear reduction mechanism reducing an output rotation of themagnet to rotate a driver. The drive mechanism may further include anouter housing coupled to the inner housing by an engagement of thedriver with the outer housing and a sliding bearing that engages theouter housing and the inner housing to prevent the inner housing fromspinning freely within the outer housing. Rotation of the magnetassembly causes the gear reduction mechanism to rotate the driver tocause the inner rod to move along a longitudinal axis substantiallywithout rotation relative to the outer housing.

In accordance with yet other implementations, there is provided agrowing rod that includes an outer housing and an inner housing disposedwithin the outer housing. The inner housing may include a magnetassembly including a magnet having a first pole and a second pole, and agear reduction mechanism coupled to the magnet within the inner housing.A first rod is secured to the inner housing and a second rod is securedto the outer housing. The gear reduction mechanism reduces an outputrotation of the magnet to rotate a driver that operates to move theinner housing along a longitudinal axis with respect to the outerhousing.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the detaileddescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofseveral implementations of the device and methods of the presentapplication, will be better understood when read in conjunction with theappended drawings. For the purposes of illustrating the growing rod ornon-fusion scoliosis expandable spinal rod of the present application,there are shown in the drawings several implementations. It should beunderstood, however, that the application is not limited to the precisearrangements and instrumentalities shown. In the drawings:

FIG. 1A illustrates a perspective view of a growing rod or non-fusionscoliosis expandable spinal rod in accordance with the presentdisclosure;

FIG. 1B illustrates a cross-sectional view of growing rod or non-fusionscoliosis expandable spinal rod of FIG. 1A;

FIGS. 2A and 2B illustrate exploded views of the growing rod ornon-fusion scoliosis expandable spinal rod of FIGS. 1A and 1B;

FIGS. 3A and 3B illustrate an exploded view and cross-sectional view,respectively, of a magnet assembly;

FIGS. 4A-4I illustrate several views of magnetic activation of a magnetof the growing rod of FIGS. 1A and 1B;

FIGS. 5A and 5B illustrate a perspective view and exploded view,respectively, of a first stage planetary gearset;

FIGS. 6A and 6B illustrate a perspective view and exploded view,respectively, of a second stage planetary gearset;

FIGS. 7A, 7B and 7C illustrate additional details of the growing rod ofFIGS. 1A and 1B; and

FIGS. 8A, 8B and 8C illustrate several views of lengthening of thegrowing rod of FIGS. 1A and 1B.

DETAILED DESCRIPTION

Certain terminology is used in the following description for convenienceonly and is not limiting. The words “right”, “left”, “lower” and “upper”designate directions in the drawings to which reference is made. Thewords “inwardly” or “distally” and “outwardly” or “proximally” refer todirections toward and away from, respectively, the patient's body, orthe geometric center of the several implementations of the non-fusionscoliosis expandable spinal rod and related parts thereof. The words,“anterior”, “posterior”, “superior,” “inferior”, “lateral” and relatedwords and/or phrases designate preferred positions, directions and/ororientations in the human body to which reference is made and are notmeant to be limiting. The terminology includes the above-listed words,derivatives thereof and words of similar import.

Referring to FIGS. 1-7, a growing rod 100 in accordance withimplementations of the present disclosure includes a first rod 102, anouter housing 106, an inner housing 108, and a second rod 104. A magnetassembly 300 and a gear reduction mechanism 124 are disposed within theinner housing 108. As will be described below, rotation of the magnetassembly 300 drives the gear reduction mechanism 124, which drives athreaded driver 214 within the outer housing. The rotation of thethreaded driver 214 causes the inner housing to move along alongitudinal axis with respect to the outer housing, thus extending (orretracting the growing rod).

With reference to FIGS. 3A-3B, the magnet assembly 300 includes a magnetcover 302, a magnet 110, a cover lid 304 and a gear wheel 306. Themagnet 110 includes a pair of opposing flats 308 that receive the coverlid 304 during assembly. The magnet 110 may be made out of Neodym andmay optionally include a protective epoxy layer. The protective layermay also be made from gold or silver and have a copper or nickel underlayer. To assemble the magnet assembly 300, the magnet 110 may be pressfit within the magnet cover 302 and the cover lid 304 may be press fitto be received by the flats 308 to enclose the magnet cover 302. Oncethe cover lid 304 is positioned, it may be welded to the magnet cover302 to seal the magnet assembly 300. The magnet assembly 300 may besealed in such a manner in order to prevent any materials or liquid fromcontacting the magnet 110 and to provide for biocompatibility. As shown,the cover lid 304 forms a keyed slot 310 into which complementary-shapedshaft portion 312 of the gear wheel 306 is received to form the completemagnet assembly 300.

The magnet 110 can be in any shape (e.g. round, square, hexagonal,octagonal etc.) so long as it fits within the magnet cover 302. As shownin FIGS. 4A-4I, the magnet 110 can be formed having a hollowed centerwith diametric poles, can be massive with diametric poles, can havemultiple diametrical poles, etc. As shown, by applying a magnetic fieldfrom an external magnet, the magnet 110 will be urged to rotate in apredetermined direction.

As shown in FIGS. 1, 2, 5 and 6, the gear reduction mechanism 124 isprovided within the inner housing 108. The gear reduction mechanism 124includes at least a two stage assembly of planetary gearsets. It isnoted that other gear arrangements may be used, and planetary gearsetsare shown as an exemplary implementation. A first stage 204A/204B isshown in FIGS. 2B, 5A and 5B. The first stage 204A/204B includes acarrier 504 that receives, e.g., four (or other number) planet gears 502that each rotate on a mount 500 that is press fit into the carrier 504.A sun gear 506, having a slotted shaft 510, is received within acomplementary slotted recess 508 formed in face the carrier. The firststage 204A/204B may be used as an input to the gear reduction mechanism124.

In some implementations, such as shown in FIG. 2B, more than one firststage 204A/204B may be included in the gear reduction mechanism 124 toachieve a desire reduction. In some implementations, the first stage isdesigned such that a plurality of first stages may be connected inseries. In such an arrangement, as shown in FIG. 7B, the planet gears ofa subsequent first stage is driven by the sun gear of a preceding firststage.

As shown in FIGS. 2B, 6A and 6B, a second stage 206 includes a carrier604 that receives, e.g., four (or other number) planet 602 gears thateach rotate on a mount 600 that is press fit into the carrier 604. Thenumber of gears in the second stage 206 is the same as the numberprovided in the first stage 204A/204B. The face of the carrier 604 inthe second stage 206 includes a catch 612. The catch 612 has a roundbase 606, a midsection 608 having hexagonal cross-section and a circularupper section 610 separated from the midsection 608 by an annular recess614. The second stage 206 may be used as an output of the gear reductionmechanism 124.

Thus, the assembled gear reduction mechanism 124 may include, e.g.,three stages. However, any number of sections may be provided in orderto achieve a desired input reduction. For example, each stage mayprovide a 4× gear reduction. As such, the total reduction may bedetermined in accordance with the number of stages provided in the gearreduction mechanism 124. The gear ratios may be changed according to thefollowing relationship in Table 1:

TABLE 1 Gear ratio Modulus Gear ratio total Thread pitch Turns for 1 mmi m i³ P x [—] [—] [—] [mm] [—] 3.0 0.15 64.0 0.5 128.0In accordance with the above, the gear reduction mechanism 124 may beconfigured such that 128 turns of gear reduction mechanism 124 extendsor retracts the growing rod 100 by 1 mm. Other ratios may be used tocontrol the rate at which the gear reduction mechanism 124 drives thegrowing rod 100. Optionally or additionally, sizes of the gears withinthe stages may be different. For example, the stages closer to the inputmay be smaller, where the gears near the output are relatively larger.

To assemble the inner housing 108, an inner bearing 201 is placed withinthe interior space of the inner housing 108. The magnet assembly 300 isthen pressed into the inner housing 108 such that a far end of themagnet assembly 300 is received within the inner bearing 201. An outerbearing 202 is then placed in the inner housing 108 such that it isreceived by the cover lid 304 of the magnet assembly 300. Next the firststage(s) 204A/204B are inserted such that an inner first stage receivesthe gear wheel 306 of the magnet assembly 300. The gear wheel 306 of themagnet assembly 300 is a rotational input to drive the gear reductionmechanism 124. As noted above, one or more first stages may be placedinto the inner housing 108 as part of the gear reduction mechanism 124,followed by a second stage 206 as an output. The assembly of the innerhousing 108 is completed by placing a bearing shoulder 208 into theinner housing 108 that is, e.g., secured to the drive housing by pins210. As shown, four pins may be used to secure the bearing shoulder 208to the inner housing 108, but other numbers of pins may be used. Thecatch 612 of the second stage 206 protrudes through the bearing shoulder208. As a result, the magnet assembly 300 and gear reduction mechanism124 are able to rotate freely within the inner housing 108.

With reference to FIGS. 1B and 2A, to engage the inner housing 108 withthe outer housing 106, a bearing 212 is slide fit around the outercircumference of the inner housing 108 at a far end. An inner surface ofbearing 212 mates with a ribbed outer surface of the inner housing 108to prevent rotation of the bearing 212 around the circumference of theinner housing 108. A threaded driver 214 having a hexagonally-shapedcenter hole is received and mounted to the catch 612 and secured theretoby a snap-fit locking clip 216. An insert 218 is placed within the outerhousing 106 to act as a stop.

To assemble the growing rod 100, the outer housing 106 is placed overthe inner housing 108 and rotated to threadedly retract the innerhousing 108 into the outer housing 106 by cooperation of an innerthreaded surface of the outer housing 108 and the threaded driver 214.The inner housing 108 is retracted into the outer housing 106 untilreaching the insert 218. As the inner housing 108 is retracted, flats213 provided in the bearing 212 snap fit to an inner surface of theouter housing 106 to complete the assembly. Four flats may be providedwith the bearing 212. The flats serve to secure the far end of the outerhousing 106 to the inner housing 108 and to counteract the momentproduced by the inner housing 108 as it rotates. Thus, the flats 213prevent the inner housing 108 from spinning freely within the outerhousing 106.

Referring now to FIGS. 1B and 2A, the first rod 102 is secured to theinner housing 108 by the threaded pins 222A/222B that engage acircumferential recess 116. A rounded end 118 of the first rod 102 hasat least one flat surface that is received by a complementary flatsurface within the inner housing 108 to prevent rotation of the firstrod 102 with respect to the inner housing 108. In some implementations,the threaded pins 222A/222B are inserted into threaded holes 220 of theinner housing 108 from the inside of the inner housing 108. Eachthreaded pin 222A or 222B includes a locking surface that engages aledge of a respective threaded hole 220 to prevent the threaded pin fromfalling out of the inner housing 108. The threaded pins 222A/222B may bescrewed from the outside using an appropriate tool to secure the firstrod 102 within the inner housing 108.

The second rod 104 is secured to the outer housing 106 by the threadedpins 226A/226B that engage a circumferential recess 120. A rounded end122 of the second rod 104 has at least one flat surface that is receivedby a complementary flat surface within the outer housing 106 to preventrotation of the second rod 104 with respect to the outer housing 106.Similar to the inner housing, the threaded pins 226A/226B used in theouter housing 106 may be inserted into the threaded 224 holes from theinside. Each threaded pin 226A or 226B may include a locking surfacethat engages a ledge of a respective threaded hole to prevent thethreaded pin from falling out of the outer housing 106. The treaded pins226A/226B may be screwed from the outside using an appropriate tool tosecure the second rod 104 within the outer housing 106.

Thus, in view of the assembly noted above the completed, assembledgrowing rod 100 may be exemplified by that illustrated in FIGS. 1A and1B. The growing rod and its components may be constructed of titanium ortitanium alloys but are not so limited and may be constructed of cobaltchromium material, polymeric materials or nearly any bio-compatiblematerial. Such materials should be relatively strong and stiff, able totake on the general size of the growing rod and its components and ableto withstand normal operating conditions of the growing rod. Thebearings and the insert may be constructed of a Polyether ether ketone(PEEK) material that is biocompatible and has a relatively lowcoefficient friction. The bearings are not limited to constructionsutilizing PEEK materials and may be constructed of nearly any materialthat permits the associated parts to rotate (e.g., ball bearings). Theouter housing 106 and the inner housing 108 may be made from anymaterial that does not exhibit magnetic properties, in order to allowthe magnetic field of the external magnet to pass there through toaffect the magnet 110 within the growing rod.

In some implementations, the outer surface of the growing rod 100 may bepolished to substantially remove any rough surfaces to reduce thelikelihood that the body will attach to the growing rod. A coating maybe placed on the growing rod for a similar purpose. In yet otherimplementations, the magnet assembly 300 may be replaced by an electricmotor that rotationally drives the gear reduction mechanism 124.

To actuate the growing rod 100 to expand within, e.g., a patientundergoing treatment, an external magnet may be used as a source of amagnetic field to cause rotation of the magnet 110. As show in FIG. 8,the growing rod initially have a contracted length. Upon excitation bythe external magnetic field, the magnet assembly 300 drives the gearreduction mechanism 124 to rotate the threaded driver 214. As thethreaded driver 214 rotates, the inner housing is driven outwardly bycooperation of the threaded driver 214 and the inner threaded surface ofthe outer housing 106 to laterally drive the inner housing 108 withrespect to the outer housing 106.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisdisclosure is not limited to the particular embodiments disclosed, butit is intended to cover modifications within the spirit and scope of thepresent disclosure as defined by the present description.

What is claimed:
 1. A growing rod, comprising: an outer housing; an inner housing disposed within the outer housing; a magnet assembly rotatably mounted within the inner housing, the magnet assembly including a magnet having a first pole and a second pole; a gear reduction mechanism coupled to the magnet within the inner housing, the gear reduction mechanism reducing an output rotation of the magnet to rotate a driver that operates to move the inner housing along a longitudinal axis with respect to the outer housing, the gear reduction mechanism including an output catch extending from the gear reduction mechanism, the output catch including a cylindrically-shaped base, a cylindrically-shaped upper section, and a shaped midsection for engaging the driver; a first rod attached to the inner housing; and a second rod attached to the outer housing.
 2. The growing rod of claim 1, wherein the first rod moves along the longitudinal axis substantially without rotation relative to the first rod.
 3. The growing rod of claim 1, the gear reduction mechanism further comprising: a first stage comprising a planetary gearset; and a second stage comprising a planetary gearset that receives the first stage, the second stage being an output of the gear reduction mechanism.
 4. The growing rod of claim 3, the magnet assembly further comprising a gear wheel, wherein the gear wheel is received by the first stage to drive the gear reduction mechanism upon rotation of the magnet assembly.
 5. The growing rod of claim 4, wherein the output catch rotates approximately one-sixty-fourth of a rotation for each full rotation of the gear wheel.
 6. The growing rod of claim 4, wherein rotation of gear wheel is transmitted by the gear reduction mechanism to rotate the driver, wherein the driver engages an inner threaded surface of the outer housing to drive the inner housing along the longitudinal axis with respect to the outer housing.
 7. The growing rod of claim 1, wherein the inner housing is moved relative to the outer housing by passing a magnetic field in proximity to the growing rod to cause the magnet to rotate about a longitudinal axis of the growing rod.
 8. The growing rod of claim 1, further comprising a bearing that is slide fit around an outer circumference of the inner housing, wherein an inner surface of bearing mates with a ribbed outer surface of the inner housing, wherein the bearing includes a plurality of flats that snap fit to an inner surface of the outer housing, wherein the plurality of flats prevent the inner housing from spinning freely within the outer housing.
 9. The growing rod of claim 1, wherein the magnet assembly includes a magnet cover that receives the magnet, and wherein the magnet includes opposing flats to which a cover lid is received to enclose the magnet cover.
 10. The growing rod of claim 9, wherein the cover lid receives a gear wheel that drives the gear reduction mechanism.
 11. The growing rod of claim 1, the inner housing further comprising: an inner bearing that is disposed within an interior space of the inner housing, the inner bearing receiving the magnet; an outer bearing that it is received by a cover lid of the magnet assembly; and the gear reduction mechanism.
 12. The growing rod of claim 1, wherein the first rod is secured to the inner housing by threaded pins that engage a circumferential recess of the first rod, and wherein a rounded end of the first rod has at least one flat surface that is received by a complementary flat surface within the inner housing to prevent rotation of the first rod with respect to the inner housing.
 13. The growing rod of claim 12, wherein the threaded pins engage the inner housing from an inside of the inner house, and wherein the threaded pins are stopped from the inside of the inner housing from falling out of the inner housing.
 14. The growing rod of claim 1, wherein the second rod is secured to the outer housing by threaded pins that engage a circumferential recess of the second rod, and wherein a rounded end of the second rod has at least one flat surface that is received by a complementary flat surface within the outer housing to prevent rotation of the second rod with respect to the outer housing.
 15. The growing rod of claim 14, wherein the threaded pins engage the outer housing from an inside of the outer house, and wherein the threaded pins are stopped from the inside of the outer housing from falling out of the outer housing.
 16. The growing rod of claim 1, wherein the catch includes an annular recess extending between the midsection and the upper section.
 17. The growing rod of claim 16, wherein the driver is mounted to the catch and includes an opening sized to receive the shaped midsection of the catch, wherein rotation of the gear wheel is transmitted by the gear reduction mechanism to rotate the driver by interaction between the opening of the driver and the shaped midsection of the catch.
 18. The growing rod of claim 17, wherein the shaped midsection defines a hexagonal-shaped cross-section and the opening of the driver defines a hexagonal-shaped opening.
 19. The growing rod of claim 17, further comprising: a locking clip sized and configured to engage the annular recess of the catch, wherein engagement between the locking clip and the catch secures the threaded driver onto the catch, wherein an outer diameter of the base of the catch is larger than an outer diameter of the midsection of the catch, such that axial movement of the driver is limited between an edge of the catch defined between the base and midsection and the clip.
 20. The growing rod of claim 1, the inner housing further comprising: a bearing shoulder secured to the inner housing to retain the magnet assembly and the gear reduction mechanism within the inner housing such that the magnet assembly and gear reduction mechanism rotate freely within the inner housing, the bearing shoulder secured to the inner housing by a pin, the bearing shoulder including a ledge extending around a perimeter of the bearing shoulder sized and configured to contact an end of the inner housing. 